Optical fiber termination device

ABSTRACT

An optical fiber termination device wherein temperature rise is minimized when light power is high or a power laser is used therewith. A first optical fiber is connected to a second optical fiber by fusing the core of the first optical fiber to the clad of the second optical fiber with a discharge generated between electrodes. The first optical fiber is inserted into a hole at the center of a ferrule and then the first optical fiber is fastened to the ferrule by fusing them. Thereafter, the edge surface of the ferrule is finished by polishing it. The second optical fiber is covered with a protective cover. Light coming from the core of the first optical fiber is incident on and scattered into the clad of the optical fiber. The light reflected toward the light source is greatly decreased by this structure.

BACKGROUND OF THE INVENTION

The present invention relates to an optical fiber termination deviceused in an optical fiber communication circuit, and especially to anoptical fiber termination device wherein a temperature rise is caused byhigh light power being terminated after passing through an optical fiberconnected thereto.

If, in the prior art, one of a pair of optical fiber connector plugsused to optically connect optical fiber communication circuits togetheris detached from the other a light signal coming from a light sourceconsisting of a laser device may reflect at the edge surface of theoptical fiber built in the optical fiber connector plug to be connectedto the light source, and the reflected light goes back to the lightsource. This type of reflection causes the laser diode to operateunstably since the reflected light is recombined with the light beinggenerated in the light source.

The reflected light energy is remarkable, and is -12 dB with respect toincident light energy when the surface of the optical fiber at the edgethereof is orthogonal to the optical axis.

The optical fiber termination device is connected to the optical fiberedge in order to scatter the light going out of the optical fiber coreso that the light signal might not reflect from the edge surface of theoptical fiber.

FIGS. 5(a), 5(b) and 5(c) show cross-sectional views of an optical fibertermination device built in accordance with the technique in the priorart, as an example, which is to be used with the optical connector.

Optical fiber 22 is inserted into hole 23 at the center of opticalconnector ferrule 21 to be connected to the light source, and rear edgesurface 24 of optical connector ferrule 21 is finished at right anglewith respect to hole 23 by polishing optical fiber ferrule 21 andoptical fiber 22 together.

Optical fiber termination device 25 consists of another ferrule andoptical fiber 26 inserted into hole 28 at the center of that ferrule.The front edge surface of optical fiber termination device 25 isfinished at right angle with respect to said hole 28 so that the frontedge surface of optical fiber termination device 25 may contact the rearedge surface of optical connector ferrule 21. Rear edge surface 30 ofsaid optical fiber termination device 25 is finished by polishing it atan angle greater than 8 degrees(or the threshold) with respect to aplane perpendicular to the optical axis of hole 28.

Consider that optical fibers 22 and 26 are inserted into alignmentsleeve 31 after the rear edge surface of optical fiber ferrule 21 iscontacted with front edge surface 29 of the other optical fiber ferrule.Light La is incident on core 32 of optical fiber 26 passing through core35 of optical fiber 22 and is reflected from edge surface 30. Thereflected light is scattered into clad 33 which surrounds core 32, asindicated by arrow Lb. This type of structure reduces the light energyreflecting from the rear edge surface of the optical fiber, and thelight energy going into the light source can be reduced by -60 dB ormore.

High light power is considered to be applied to the optical fibertermination device having such a structure as shown in FIGS. 5(a), 5(b)and 5(c) which are used to reduce the reflection of the light at therear edge surface thereof where the light is to be terminated. Thetemperature of the optical fiber termination device rises around therear edge surface thereof, at which the light energy can reflect, due tothe scattering of the light into the clad layer. The temperature risesometimes destroys the optical fiber termination device.

The objective of the present invention is therefore to provide theoptical fiber termination device having a new type of structure which isfree from temperature rise when used in high power light signalcircuits.

SUMMARY OF THE INVENTION

The optical fiber termination device built in accordance with thepresent invention is constructed by fusing the rear edge surface(s) ofthe core(s) of first optical fiber(s) through which the light signal tobe terminated can pass to the front edge surface(s) of the clad(s) ofsecond optical fiber(s).

The optical fiber termination device can be of such a structure thatfirst and second optical fibers are respectively arranged in line toform a ribbon consisting of a plurality of optical fibers, and that thetermination is accomplished by fusing the rear edge surfaces of thecores of first optical fibers through which the light signals to betransmitted can pass to the front edge surfaces of the clads of secondoptical fibers.

The optical fiber termination device is of such a structure that firstand second optical fibers are covered with a protective cover and thatthe inner surface of the protective cover can absorb or scatter thelight reflected from the rear edge surface(s) of second optical fiberswhen the reflected light strikes said inner surface thereof.

The optical fiber termination device built in accordance with thepresent invention is free from local temperature rise since the lightpassing through the core(s) of first optical fiber(s) to be connected tothe light source goes to the clad(s) of second optical fiber(s) to beterminated.

The optical fiber termination device built in accordance with thepresent invention is of such a structure that second optical fiber(s)made as a part of first optical fiber(s) to be connected to the lightsource is(are) easily fused to the first optical fiber(s) after thefirst optical fiber(s) is(are) cut to yield second optical fiber(s) andaligned to the second optical fiber(s).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view for describing an optical fibertermination device built in accordance with the present invention, whichindicates the procedure for fusing a pair of optical fibers togetherduring fabrication of the optical fiber termination device.

FIG. 2 shows a cross-sectional view of a first embodiment of an opticalfiber termination device wherein a pair of optical fibers are connectedtogether by fusing them.

FIG. 3 shows a cross-sectional view showing the use of theabove-mentioned optical fiber termination device built in accordancewith the present invention wherein the optical connector ferrule to beconnected to the light source is used to align optical fibers.

FIGS. 4(a) and 4(b) show another embodiment of the optical fibertermination device built in accordance with the present inventionwherein a plurality of first and second optical fibers are arranged inline and connected together to form a pair of ribbons, each consistingof the first or second optical fibers. FIG. 4(a) is a cross-sectionalview thereof and FIG. 4(b) a side view thereof.

FIGS. 5(a), 5(b) and 5(c) show cross-sectional views of a prior artoptical fiber termination device used together with an opticalconnector. FIG. 5(a) is a cross-sectional view of the device, and FIGS.5(b) and 5(c) are cross-sectional views of the optical fiber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail referring to thedrawings.

FIG. 1 shows a cross-sectional view of an optical fiber terminationdevice built in accordance with the present invention, which indicatesthe procedure for fusing a pair of optical fibers together duringfabrication of the optical fiber termination device.

Referring to FIG. 1, a first optical fiber 1 is faced to a secondoptical fiber 2 with axis O of core 1a and axis O' of core 2aoff-centered so that core 1a of first optical fiber 1 is attached toclad 2b of second optical fiber 2 and clad 1b is attached to core 2a.The junction between first optical fiber 1 and second optical fiber 2 isfused by an arc discharge 5 generated across electrodes 3 and 4. Aheater can be used in place of the arc discharge if desired.

FIG. 2 shows a cross-sectional view of a first embodiment of the opticalfiber termination device wherein a pair of optical fibers are connectedtogether by fusing form a fusion splice in accordance with the methoddescribed above.

Referring to FIG. 2, first optical fiber 1 is inserted into hole 6b offerrule 6 at the center thereof and is fastened therein by an adhesiveagent. Front edge surface 6a of ferrule 6 is finished by polishing it.

No special work is needed to finish the rear edge surface of secondoptical fiber 2, wherefrom the light coming from clad 2b can scatter.The rear edge surface of second optical fiber 2 should remain roughwithout any work other than the cutting thereof.

Second optical fiber 2 is covered with a protective cover 7, andprotective cover 7 having a cavity therein is preferably made by moldinga plastic material to form such a structure that it can absorb the lightcoming from second optical fiber 2.

Inner bottom surface 7a of protective cover 7 curves outward or inclineswith respect to optical axis O' so that the light reflecting from saidinner bottom surface 7a does not strike rear edge surface 2c of clad 2b.

This type of structure reduces the energy density of the light goinginto clad 2b from core 1a to -20 dB or so. That is, light L coming fromthe light source passes through core 1a of first optical fiber 1 and isstraightly incident on clad 2b of second optical fiber 2. The lightincident on clad 2b scatters into clad 2b. The scattering of the lightinto clad 2b of second optical fiber 2 reduces the power density of thelight in clad 2b. The light power goes out of clad 2b of second opticalfiber 2 into the area enclosed by protective cover 7, and little lightpower can return to the light source.

The light power returning to the light source due to the reflection wasless than -60 dB in the embodiment shown in FIG. 2. The temperature risewithin the optical fiber termination device due to light powerabsorption was lower than the minimum threshold of the detector.

FIG. 3 shows a cross-sectional view of the optical fiber terminationdevice built in accordance with the present invention wherein opticalconnector ferrule 9 to be connected to the light source is used to alignoptical fibers. Optical connector ferrule 9 is inserted into alignmentsleeve 8 moving from the left to right, and optical fiber terminationdevice 10 built in accordance with the present invention is insertedinto alignment sleeve 8 from the other side.

FIGS. 4(a) and 4(b) show another embodiment of the optical fibertermination device built in accordance with the present inventionwherein a plurality of first and second optical fibers are arranged inline and connected together to form a pair of ribbons, each consistingof the first or second optical fiber.

A plurality of optical fibers are fused in accordance with the procedureshown in FIG. 1. and they are inserted into the respective holes offerrule 11 so as to form a ribbon of optical fibers. They are thencovered with protective cover 14.

In FIGS. 4(a), 4(b), the optical fiber termination device consisting offour optical fibers is shown. First optical fiber array 12 consists offour optical fibers and second optical fiber array 13 of another fouroptical fibers.

As described above, the optical fiber termination device built inaccordance with the present invention is constructed by coaxiallyaligning and fusing the core(s) of first optical fiber(s) to beconnected to the light source to the clad(s) of second optical fiber(s)to be terminated so that the light power passing through the core(s) ofthe first optical fiber(s) can enter and straightly be diffused into theclad(s) of the second optical fiber(s). The light power within theclad(s) of the second optical fiber(s) is much lower than that withinthe core(s) of the first optical fiber(s) since the dimensions of theclad(s) are much greater than those of the core(s). This type of opticalfiber termination device is free from internal temperature rise, and thereflection losses are much less than those of the optical fibertermination device built in accordance with the prior art technique

The optical fiber termination device built in accordance with thepresent invention can be constructed by a fusing method employing an arcdischarge which is a simple process not requiring the polishing of thesurface edges of the ferrule. The optical fiber termination device canthus be constructed with reduced cost, and the fabrication process issimpler than the conventional process. The technique of fusing a ribbonconsisting of a plurality of optical fibers to another ribbon consistingof another plurality of optical fibers at a time has been establishedelsewhere, and the optical fiber termination device built in accordancewith the present invention can also be constructed with reduced cost.The fabrication process in this case is also simpler than theconventional process.

The fabrication process of the optical fiber termination device built inaccordance with the present invention can be applied to construct anoptical division and multiplication device, an optical switch and manyother devices.

What is claimed is:
 1. An optical fiber termination device, comprisingafirst optical fiber for receiving light from a light source, said firstoptical fiber having a first core extending along a first optical axisand a first clad surrounding said first core; a second optical fiber forreceiving light from said first optical fiber, said second optical fiberhaving a second core extending along a second optical axis offset fromsaid first optical axis and a second clad surrounding said second core,an end portion of the first core of said first optical fiber being fusedto an end portion of the second clad of said second optical fiber and anend portion of the second core of said second optical fiber being fusedto an end portion of the first clad of said first optical fiber to forma fusion splice; and a protective cover having a cavity thereinsurrounding said second optical fiber, said protective cover being madeof light absorbing material for absorbing light emanating from saidsecond optical fiber, whereby light power returned to the light sourceand a temperature rise within said termination device are minimized. 2.An optical fiber termination device as claimed in claim 1, wherein thecavity of said protective cover has a surface element, said surfaceelement having a curvature such that light reflected therefrom does notimpinge on a rear edge surface of said second clad.
 3. An optical fibertermination device as claimed in claim 2, wherein the surface element ofsaid cavity projects toward said second optical fiber, and issubstantially symmetrical with respect to said first optical axis.
 4. Anoptical fiber termination device as claimed in claim 1, wherein the endportions of said first and second cores at said fusion splice areparallel to each other.
 5. An optical fiber termination device asclaimed in claim 1, which further comprises a ferrule surrounding saidfirst optical fiber, said ferrule being connected to said protectivecover.
 6. An optical fiber termination device, comprisinga firstplurality of parallel optical fibers for receiving light from a lightsource, each of said first plurality of optical fibers having a firstcore extending along a first optical axis and a first clad surroundingsaid first core; a second plurality of parallel optical fibers forreceiving light from said first plurality of optical fibers, each ofsaid second plurality of optical fibers having a second core extendingalong a second optical axis offset from a first optical axis of acorresponding one of said first optical fibers and a second cladsurrounding said second core, an end portion of the first core of eachof said first optical fibers being fused to the second clad of acorresponding one of said second optical fibers and an end portion ofthe second core of each of said second optical fibers being fused to anend portion of the first clad of a corresponding one of said firstoptical fibers to form a plurality of fusion splices; and a protectivecover having a cavity therein surrounding said second plurality ofoptical fibers, said protective cover being made of light absorbingmaterial for absorbing light emanating from said second plurality ofoptical fibers, whereby light power returned to the light source and atemperature rise within said termination device are minimized.
 7. Anoptical fiber termination device as claimed in claim 6, wherein thecavity of said protective cover has a surface element, said surfaceelement having a curvature such that light reflected therefrom does notimpinge on a rear edge surface of a second clad.
 8. An optical fibertermination device as claimed in claim 6, wherein the end portions ofthe first cores of said first plurality of optical fibers are parallelto the end portions of corresponding cores of said second plurality ofoptical fibers at said fusion splices.
 9. An optical fiber terminationdevice as claimed in claim 6, which further comprises a ferrulesurrounding said first plurality of optical fibers, said ferrule beingconnected to said protective cover.
 10. The method of terminating afirst optical fiber, said optical fiber having core and clad portions,comprising the steps offusing a clad portion of a second optical fiberto the core portion of said first optical fiber, and fusing a coreportion of said second optical fiber to the clad portion of said firstoptical fiber to form a fusion splice; and surrounding said secondoptical fiber with a protective cover having a cavity therein, saidprotective cover being made of light absorbing material.